The present invention relates to a control valve driving device, and more particularly to a control valve driving device which is intended to change an opening angle (i.e. effective size) of a control valve provided in an intake or an exhaust system thereby permitting an intake or an exhaust characteristic of an engine to change.
In an internal combustion engine, for example, a piston valve type of two cycle gasoline engine, control of exhaust gas flow to an intake of an exhaust passage is made by a port of the cylinder cooperating with a piston reciprocating in this cylinder. In this two cycle engine, in order to enhance a filling efficiency of the mixing gas in the cylinder, the mixing gas is confined at high density at the intake side, while it is necessary that pushing back action is effected so as to not cause ventilation of refresh air from the cylinder at the exhaust side.
For this purpose, for example, as shown in Japanese Utility Model Application publication No. 55-132321 (132321/1980), in the two cycle engine, an exhaust pipe is formed in a chamber narrowed down at its leading end to utilize a reflecting wave of an exhaust pressure. In this case, the reflecting wave is set to reach this portion in a timing immediately before an exhaust port is closed. However, it is impossible to obtain a good pushing back action without changing from a low speed revolution region to a high speed revolution region. For this reason, in the prior art, there have been adopted various methods which adjusts a phase of a reflecting wave of intake and exhaust system by controlling pulse of an exhaust pressure.
That is, as shown in FIGS. 1 and 2, in a wall portion of a cylinder 1 there is formed an exhaust port 3 which is opened and closed by a piston 2. Near the exhaust port 3 is provided a control valve 4. Valve 4, for example, may have a half-drum shape adapted to open and close an upper portion of the exhaust port 3. Thus, the control valve 4 is driven or rotated to an open direction to hasten an exhaust timing when the revolution number of the engine has increased, in order to obtain a good driving efficiency.
In such a prior system, as shown in PCT/JP application No. 86/00671, good driving efficiency has been obtained by utilizing a pulsation of an exhaust pressure and control means which to give an optimum opening angle of the control valve 4 based on revolution number of engine or the like. However, a fact that the pulsation of the exhaust pressure is utilized means that the pressure of the pulsation is satisfying the required value.
Accordingly, when a peak pressure is generated by the pulsation, the same pressure is exerted on the control valve 4, whereby the pressing or sucking force is adapted to act on the control valve 4 in proportion to a pressure receiving area of the control valve 4. Since this force becomes such as to resist a movement of the control valve 4, a driving device driving the control valve 4 necessitates having a driving mechanism which can overcome such a resisting force.